Electrocoating process

ABSTRACT

A PROCESS FOR THE TRANSFER OF COATING MATERIAL INTO AN ELECTROCOATING BATH WHEREIN A COATED, SO-CALLED &#34;TRANSFER ELECTRODE&#34; IS IMMERSED IN AN ELECTROCOATING BATH AND THE COATING MATERIAL IS REMOVED FROM THE TRANSFER ELECTRODE AND APPLIED ONTO AN OPPOSITELY CHARGED ELECTRODE.

' Fe 23, 19 1 F. WEHRMANN ELECTROCOATING PROCESS 3 Sheets-Sheet 1 FiledMay 2, .1967

INVENTOR FELIX WEHRMANN av I ATTORNEYS Feb. 23, 1.971 F. WEHRMANNELECTROCOATING} PhocEss 3 Sheets-Sheet 2 Filed May. 2. 1967 INVENTORFELIX WEHR MANN BY HWWJM/M ATTORNEYS Filed May 2. 1967 $.Sheets-Sheet 8INVENTOR FELI X WEHRMANN BY HIM xz'za ATTORNEYS United States Patent3,565,782 ELECTRO0ATING PROCESS Felix Wehrmanu, Vienna, Austria,assignor, by mesne assignments, to Stollaek Aktiengesellschaft,Guntramsdorf, near Vienna, Austria, a corporation of Austria Filed May2, 1967, Ser. No. 635,977 Claims priority, application Austria, May 3,1966, A 4,180/ 66; Mar. 13, 1967, A 2,352/ 67; Apr. 28, 1967, A 4,002/67Int. Cl. B0lk 5/02; C23b 13/00 US. Cl. 204-181 Claims ABSTRACT OF THEDISELOSURE A process for the transfer of coating material into anelectrocoating bath wherein a coated, so-called transfer electrode isimmersed in an electrocoating bath and the coating material is removedfrom the transfer electrode and applied onto an oppositely chargedelectrode.

PRIOR ART Up to now, automatically or semi-automatically controlledmetering devices have been used to keep the solids content ofelectrocoating baths as constant as possible. However, these operationshave not been sufficiently accurate because coating material toreplenish that consumed are highly viscous pastes which have to bediluted with the bath liquor after metering thereof and before additionto the electrocoating bath. The amount of the coating material to bemetered has to be readjusted each time to conform to the analysis of thesolids content of the electrocoating bath and the resulting difiicultiesand inaccuracies cannot guarantee a satisfactory operation. Moreover,such metering devices have a high initial cost and a high operating costand call for exact chemical and physical analysis methods to ascertainthe quantities of coating agent needed to regenerate the coating bath.Great analysis difficulties particularly arise in maintaining constantcomposition in electrocoating baths having a low solids content.

Another problem in electrocoating processes arises in the losses whichoccur in the washing step. When any type of article, such as anautomobile body is lifted from the immersion electrocoating bath, aliquid film of the coating emulsion or dispersion adheres to the surfaceof the said article on to the coating applied to the article. This filmhas to be washed off before the drying and annealing process and thewashing is usually accomplished in a wash tank equipped with overheadshower heads to facilitate the rinsing process. However, the rinsed offfilm contains all of the lacquer ingredients, pigments and coatingagents used for the preparation of the electrocoating bath. Up to now,these wash waters were discarded into drains since the coating materialwas believed to be too greatly diluted for economical recovery thereof.The loss of these valuable, expensive ingredients not only considerablyincreases the cost of operation of an electrocoating plant, but the washwaters become so heavily soiled because the coating materials amount toabout 2% by weight thereof that the main drains become clogged.

OBJECTS OF THE INVENTION It is an object of the invention to provide anovel process for introducing coating material into an electrocoatingbath by means of a transfer electrode.

'ice

It is another object of the invention to provide a novel processmaintaining the solids content of an electrocoating bath constant in asimple manner.

It is a further object of the invention to provide a novel economicalelectrocoating process wherein excess coating material is recovered fromthe wash water.

It is an additional object of the invention to provide novel apparatusfor maintaining the solids content of electrocoating baths constantwithout expensive metering devices.

It is another object of the invention to provide novel apparatus forrecovering excess coating material from wash waters for reuse in theelectrocoating process.

These and other objects and advantages of the invention will becomeobvious from the following detailed description.

THE INVENTION The novel process of the invention for transferringcoating material into an electrocoating bath comprises immersing atransfer electrode coated with the coating material in an electrocoatingbath and removing the coating agent from the transfer electrode andapplying it to a counter electrode. With an anodically depositablecoating material, the transfer electrode acts as a cathode in theelectrocoating bath and with a cathodically depositable coatingmaterial, the transfer electrode acts as an anode in the electrocoatingbath.

When using the process of the invention to maintain the solids contentconstant in an electrocoating bath without the use of metering devicesthe transfer electrode, which may be one or several electrodes, isimmersed in a supply vessel containing additional coating material, anelectric charge is applied to the transfer electrode so that the coatingmaterial is deposited on the transfer electrode, the transfer electrodeis then immersed in the elec trocoating bath wherein the electrocoatingmaterial is removed from the transfer electrode and deposited on anoppositely charged electrode which may be the objects to be coated or astationary electrode in the electrocoating bath. The surface area of thetransfer electrode is such that the amount of the coating materialtransferred is sufficient to coat a predetermined number of articles.

The process may be effected in an anhydrous and/ or aqueous mediumdepending upon the type of coating material being employed. Therefore,both the supply bath and the electrocoating bath may be aqueous oranhydrous solutions, suspensions or dispersions of the coating materialor one bath may be aqueous and the other bath may be anhydrous.

The composition of the coating material in the supply bath is selectedso that the coating material removed from the transfer electrode in thecoating bath has the same composition as that required as a feedsolution. The solids content of the liquid coating compositions may bethe same in both baths but a higher solids content is preferablymaintained in the supply bath than that in the electrocoating bath. Inthe electrocoating bath, the solids content may be 0.1 to 45% by weightof the bath, but the solids content in the supply bath may be 0.1 to byweight. The transfer electrode may also be coated by various physicaland chemical methods, such as immersion.

This process makes it possible for the first time to operate theelectrocoating bath at a very low solids content since the compositionthereof can be accurately controlled which reduces any loss of coatingmaterial during the rinsing process to a minimum not previouslypossible. An additional great advantage of the low solids content in theelectrocoating bath is that it is constantly recycled whereby nodecomposition reactions of the synthetic resin binders and the like willoccur. Because fresh coating material equal to that applied to theoppositely charged electrode is being continuously supplied to theelectrocoating bath, the pH value of the bath adjusts itself to anequilibrium due to the simultaneous addition and consumption of acids orbases present therein. Also, no care of the electrocoating bath or thereplenishment of water or solvent is required. When a high content oforganic solvent is used, it is possible to employ a coating materialadditive wtih a solids content of 70%.

The electrical circuits for the electrocoating bath and the supply bathfor coating the transfer electrode may be operated separately or inseries or parallel relation to each other. The voltages may range from0.1 to 100,000 volts.

When using the process of the invention to recover coating material fromthe wash waters used to rinse the electrocoated objects before drying, adirect current is passed through the Wash waters having immersed thereina transfer electrode whereby coating material in the wash Water isdeposited thereon and the coated transfer electrode is passed to theelectrocoating bath wherein the voltage on the counter electrode isgreater than that on the transfer electrode and the coating material isremoved from the transfer electrode, and combines with the bath liquor.Again in this process, the transfer electrode acts as an anode orcathode in wash water and in the reverse sense in the electrocoatingbath depending on whether the coat-' ing material is anodically orcathodically deposited. The opposite electrode in the electrocoatingbath may be in the articles to be coated or a stationary electrode inthe electrocoating bath.

The transfer electrodes in this process preferably have as large asurface area as possible due to the great dilution of the coatingmaterials in the Wash water. The dimension of the transfer electrodes ismore or less adapted to the width of the baths and the electrodespreferably have a grooved or corrugated net-like roughened surface. Thetransfer electrodes can be one or a series of plate electrodes or may bea continuous electrode with one loop of the electrode in the wash watersand a second loop of the electrode in the electrocoating bath.

This variation of the process of the invention has the advantage thatall of the coating material is recovered from the wash water so that thediscarded wash water is not polluted and otherwise lost coating materialis recovered which greatly reduces the cost of the electrocoatingoperation.

When using a continuous transfer electrode, the applied voltages areselected so that the lowest voltage is applied to the 'wash bath or acounter electrode in the wash bath and the highest voltage is applied tothe article to be coated which acts as the counter electrode in theelectrocoating bath while the continuous moving electrode has a voltagebetween the two baths so that it will act as an anode in the wash bathand as a cathode in the electrocoating bath. Preferably, the voltagedifference between the counter electrode in the wash tank and thecontinuous moving electrode and between the continuous moving electrodeand the article to be coated is within the range of 150 to 200' volts.Therefore, the voltage on the counter electrode in the wash bath may be0, the voltage on the moving electrode may be +150 to 200 volts and thevoltage on the article to be coated may be +350 to 400 volts. However,by varying the circuit, the voltage on the counter electrode in the washbath may be .15O to 200 volts, the voltage on the moving electrode maybe and the voltage on the article to be coated may be +150 to 200 voltsdepending upon the requirement of the operation.

When using one or more individual transfer electrodes,

the application onto and removal of the coating material from thetransfer electrode is preferably effected at the same voltage although adifferent voltage may be used to apply the coating material to thetransfer electrode and preferably a lower voltage than that used toremove the coating material from the transfer electrode. Again,advantageous voltages are of the order of to 200 volts.

The apparatus of the invention for transferring coating material into anelectrocoating bath is comprised of a coating bath, a washing device anda supply bath and at least one continuous transfer electrode which incycles is coated with coating material in the supply bath and depositsthe coating material in the coating bath. Preferably, there is aplurality of transfer electrodes.

The transfer electrodes may be grounded and the counter electrodes inthe supply bath and in the coating bath are oppositely polarized andhave a potential greater than zero, or the article to be coated in thecoating bath may be attached to one pole of a direct current source, thetransfer electrode may be fed by voltage division and the counterelectrode in the supply vessel has a zero potential.

In one embodiment of the invention, the individual members of theapparatus are constructed or installed so that the full cross-sectionalarea of the immersion bath may be used for the coating of the variousarticles. The said apparatus is characterized in that it consists of twogrounded suspension trolleys forming a common branch across two switchpoints which leads into the coating bath and across the said commonbranch, the articles to be coated and the large surface area electrodeswhich have been coated in the wash water collecting bath areindividually conveyed into the coating tank. For technical reasons, thewash and rinsing baths should be disposed immediately adjacent to thecoating bath to prevent the liquid film which adheres to the articleafter having been lifted out of the coating tank, from drying on thesurface of said article. The gradually accumulating rinsing or washwater is pumped into a water collecting bath, after a certainconcentration has been attained. One loop of the suspension trolley isguided into this tank which may be set up at any desired location, andthe large surface area transfer electrodes are immersed in the washwater collecting tank by this loop.

The two switch points of the apparatus are constructed as pole selectorswitches, which has the effect that while passing the article to becoated across the first switch point, the electric selector switches ofboth switch points and the insulated electrodes in the coating bath areconnected with one pole, for example, the negative pole of the rectifieraggregate. When the coated article leaves the immersion tank and passesover the second switch point, the electric selector switches of bothswitch points connect the electrodes with the other pole, for example,the positive pole of the rectifier aggregate. When immediatelythereafter, a second article is to be coated, the process of switchingwill be repeated. However, when an electrode which has been coated inthe wash water collecting tank is guided across the first switch pointonto the common branch of the suspension trolley, the insulatedelectrodes present in the coating tank remain connected with the samepole, for example, the positive pole of the rectifier aggregate, so thatthe coating on the electrode can be removed in the coating tank and thusis recovered. When the large surface area transfer electrode, freed ofthe coating film, leaves the coating tank and passes across the secondswitch point the electrodes present in the coating vessel becomeconnected again with the first pole, for example, the negative pole ofthe rectifier aggregate by means of the selector switches of the twoswitch points.

By this electrical switch operation, simple conductive suspension rods,in contrast to the previously used susgension rods equipped withinsulating means, can be used for the conveyance of articles to becoated as well as of large surface area transfer electrodes. This meansan additional, substantial simplification of the apparatus while at thesame time guaranteeing absolute safety against electrical shocks byaccidentally touching any of the individual elements of the apparatus.

To conduct the removal process in the wash water collecting bath in astatic-free manner, the counter electrodes present therein, are enclosedin a well known manner in diaphragm cells. A further modification of theinvention is not only to ground the two suspension trolleys, but alsoboth baths as well as the neutral point of the rectifier aggregate ofthe alternating current. It is also advantageous to insulate, in theusual manner, the coating and the wash water collecting baths by coatingthe interior walls of these tanks in order to prevent any deposits ofthe coating material along these walls. Because of the very lowconcentration of the coating materials in the rinsing water, electrodesof the largest possible surface area are used for the recovery of thecoating material. The dimension of the electrodes is adapted more orless to the dimension of a cross-section of the coating bath and theseelectrodes may have a corrugated, grooved, mesh-like roughened surface.These electrodes act in reverse sense to those in the coating tank.

Referring now to the schematic drawings:

FIG. 1 illustrates an embodiment of the invention in which the solidscontent of the electrocoating bath is maintained constant and thetransfer electrode and article to be coated are immersed simultaneouslyin the electrocoating bath.

FIG. 2 illustrates an embodiment wherein the solids content of theelectrocoating bath is maintained constant in which a counter electrodeis employed in the electrocoating bath.

FIG. 3 illustrates an embodiment of the invention wherein the coatingmaterial from the wash waters is transferred to the electrocoating bathby means of a moving, continuous electrode.

FIG. 4 illustrates an embodiment of the invention wherein the coatingmaterial is transferred from the wash water to the electrocoating bathby transfer electrodes which pass alternatively into the electrocoatingbath with the article to be coated.

In the embodiment of FIG. 1, the apparatus is comprised of anelectrocoating bath 3 and a supply bath which are connected by acontinuous suspension trolley 1 which conveys transfer electrodes 2 oninsulated suspension rods. The transfer electrodes 2 are movably spacedat such a distance from one another that when one uncoated transferelectrode 2 is immersed in supply bath 4 provided with counter electrode4a, a coated transfer electrode 2 is immersed in electrocoating bath 3and a third coated transfer electrode 2 is simultaneously washed in arinsing device 6. Simultaneous with the immersion of transfer electrodes2 in the supply and electrocoating baths, an article 5 to be coated isconveyed by suspension trolley 7 for immersion of the article 5 in theelectrocoating bath. The electric current is applied so that theuncoated transfer electrode 2 in the supply bath 4 acts as an anode withcounter electrode 4a acting as the cathode whereby the said transferelectrode is coated with the coating material while the coated transferelectrode '2 in the electrocoating bath 3 acts as a cathode with thearticle 5 to be coated acting as an anode. This permits the same amountof coating material to be added to the electrocoating bath from transferelectrode 2 as is being removed therefrom by deposit on the article 5 tobe coated. By regulating the removal of the coating material from thetransfer electrode 2, the transfer electrode 2 can supply to theelectrocoating bath a sufficient amount of coating material to coat oneor more articles 5 to be coated. If more than one article 5 is to becoated by one transfer electrode 2, the transfer electrodes 2 arepreferably provided with a serrated, net-shaped or roughened surface sothat the surface area of the electrode 2 is large.

In the embodiment of FIG. 2, the transfer electrode 2 is not immersed inthe electrocoating bath simultaneously with the article 5 to be coatedand the electrocoating bath is provided with counter electrodes 8. Thetransfer electrodes 2 again are transported on insulated suspension rodson suspension trolley 1 from supply bath 4 through rinsing device 6 toelectrocoating bath 3. The coating material is removed from a coatedtransfer electrode 2 in the electrocoating bath 3 and transferred tostationary counter electrodes 8. After removal of transfer electrode 2from the electrocoating bath 3, the article 5 to be coated is conveyedby suspension trolley 7 to electrocoating bath 3. The direction of theelectric current in the electrocoating bath is reversed whereby thecoating material is transferred from stationary electrodes 8 onto thearticle 5. The number of transfer electrodes 2 may be greater or lessthan the three shown in FIGS. 1 and 2 and the transfer electrodes may becoated by a con venient means, such as, electrocoating baths, immersionmeans and other chemical and physical coating means.

In the apparatus of FIG. 3, the article 11 to be coated is immersed inthe coating composition 10 in elcctro coating bath 9 by means of trolley11a whose guide rail is connected to the positive pole of the directcurrent source supplying 400 volts. After the coating operation iscompleted, the article 11 is removed from the electrocoating compositionand passed through wash tank 12 where under currentless conditions it isfreed of any still adhering coating composition by being passed undersprayer 18. The rinsed off coating composition accumulates in washwaters 13 in wash bath 12 and the wash waters 13 have to be drained offafter a short period of operation.

A continuous metal electrode in the form of a band, chain or mesh isguided by means of guide pulleys 14 and 15 so that one loop 16 of theelectrode is immersed in wash bath 12 while the loop 17 is immersed inthe electrocoating bath 9 and the continuous electrode is driven byoperating pulley 15. In this illustration, the continuous electrode isfed with a R-R positive direct current of about 200 volts by a voltagedivider, whereas the wash tank or a counter electrode present in thesaid tank shows the zero potential. The voltage difference between zeroand 200 volts is adequate to deposit the valuable coating materialpresent in wash waters 13 on the continuous moving electrode. When thiscoating material arrives in the electrocoating bath, the voltagedifference in relation to the article to be coated, which is again about200 volts, which causes the coating material to become detached. Thesedetached coating materials then become dispersed in theelectro-immersion bath and are conveyed from these onto the article tobe coated.

In the embodiment of FIG. 4, the coating bath 19 is provided with acommon branch 2122 of two grounded suspension trolleys 21 and 22 leadinginto the said tank 19. The two switch points 25 and 25' are developed aspole selector switches which are circuit connected in a synchronizedmanner. One branch of the suspension trolley 21 leads into the washwater collecting bath 20 wherein electrodes 29 are arranged in diaphragmcells. When an article 24 to be coated is conveyed via the trolley '22across the first point 25 the insulated electrodes 28 present in thecoating tank 1 are, by means of the pole selector switches of the twoswitch points 25 and 25, connected via the circuit 31 with the negativepole 33 of the rectifier aggregate of the alternating current, wherebythe grounded article 24 acts as an anode and is coated. 'When the coatedarticle 24 leaves the immersion bath 19, the electrodes 28 in thecoating bath 19 are, while passing the second switch point 25',connected by means of the pole selector switches via the circuit 31 withthe positive pole 32 of the rectifier aggregate of the alternatingcurrent. Now, either the next article 24 to be coated can be conveyedinto the coating bath 19 with a repeating of the switching operation asdescribed, or a large surface area electrode 23 which has been coated inthe wash water collecting bath 20, can be moved across the first switchpoint 25 into the coating bath 20. The two pole selector switches leavethe electrodes 28 connected with the positive pole 32 of the rectifier.When the electrode 23, 23 has been freed of the adherent coatingmaterial and has left the said bath 19 and has crossed the second switchpoint 25, then the electrodes 28 are connected With the negative pole 33by the pole selector switches.

The articles 24, upon leaving the coating bath 19, are freed of anyadherent liquid coating film by passing under the water jets 30 disposedabove rinsing bath 26. After a predetermined concentration of thecoating material is attained in the wash water, this 'water is conveyedby pump 27 into wash water collecting bath 20, wherein the large surfacearea electrodes 23 are coated, to recover the coating materials. Whenusing cathodically removable binding agents, the circuit arrangement maybe effected so that the article 24 to be coated acts as an anode inimmersion bath 19 and so that the large surface area electrodes 23 actas anodes in immersion bath 19 and as cathodes in wash water collectingbath 20.

In the following examples there are described several preferredembodiments to illustrate the invention. However, it should beunderstood that the invention is not intended to be limited to thespecific embodiments.

EXAMPLE I A coating composition concentrate was prepared from 34 partsby weight of aluminum silicate pigment, 13 parts by weight of bariumchromate, 45 parts by weight of titanium dioxide, 3 parts by weight oftalc and 420 parts by weight of Resydrol E 450 (83% water-soluble,heathardenable electrophoresis resin). The said concentrate was dilutedwith water to a solids content of 10% by weight and was used in thesupply bath and the coating bath of FIG. 1 with a voltage of 15 volts inboth baths.

EXAMPLE II 15 parts by weight of acrylamide were dissolved in 70 partsby weight of butanol and then 8 parts by weight of acrylic acid, 25parts by weight of styrene, 25 parts by weight of butyl acrylate, 27parts by weight of ethyl acrylate, parts by weight of dodecyl mercaptanand 1 part by weight of di-tert.-butyl peroxide were added there to. Oneportion of the mixture was heated to effect polymerization and whenreflux temperatures were reached, the rest of the mixture was added overa period of 2 to 3 hours. The degree of polymerization was controlled bythe solids content. After polymerization \was complete, 12.7 parts byweight of formaldehyde were added to the clean, viscous solution and thereaction mixture was maintained at reflux until no more water ofreaction was formed (2 to 3 hours). A portion of the butanol was removedby vacuum distillation and the solution was concentrated as much aspossible. The resulting resin, after neutralization with dimethylethanolamine was watersoluble and was diluted with water to aconcentration of 60%.

A coating composition was prepared from 835.0 gm. of a 60% solution ofthe said resin, 57.0 gm. of aluminum silicate, 19.4 gm. of molybdateorange, 15.1 gm. of Permanent violet MR, 5.8 gm. of iron oxide red, 3.6gm. of titanium dioxide and 64.1 gm. of water. The concentrate watediluted with a 70:30 mixtures of ethanol and isopropyl glycol. In thecoating bath of FIG. 1, the solids content of the coating compositionwas 20% and the voltage was 140 volts and the solids content in thesupply bath was 50% and the voltage was 90 volts.

EXAMPLE III The concentrate of Example I was diluted with water to asolids content of 20% by weight for the coating composition in thesupply bath of FIG. 1 operated at a voltage of 60 volts and to a solidscontent of 1% by weight in the electrocoating bath operated at a voltageof 180 volts.

EXAMPLE IV A concentrate consisting of 3.5 parts by weight of carbonblack, 11 parts by weight of barium sulfate, 3 parts by weight of talc,19.0 parts by weight of butyl glycol, 4 parts by weight of nonanol, 12parts by weight of water and 40.8 parts by weight of Resydrol P 410 (awatersoluble plasticized, heat hardenable phenol resin) was diluted witha 20:80 mixture of ethylene glycol and ethanol. The supply bath of FIG.1 had a solids content of 40% and was operated at volts while theelectrocoating bath had a solids content of 80% and was operated at avoltage of 280 volts.

EXAMPLE V A coating material concentrate consisting of 35 parts byweight of lithopone, 3 parts by weight of tale, 9 parts by weight ofbutyl diglycol, 3 parts by weight of ethylene glycol, 9 parts by Weightof water and 34 parts by weight of Resydrol M 490 (a water-soluble,plasticized, heathardenable melamine resin) was diluted with ethanol.The supply bath of FIG. 1 had a solids content of 5% by weight and wasoperated at volts while the electrocoating bath had a solids content of0.5 by weight and was operated at 150 volts also.

EXAMPLE VI A coating bath concentrate consisting of 3 parts by weight ofcarbon black, 2 parts by weight of strontium chromate, 6 parts by weightof butyl glycol, 7 parts by weight of methylene glycol, 0.2 part byweight of diethylamine, 20 parts by weight of water and 60 parts byweight of Resydrol P 410 (water-soluble, plasticized, heathardenablephenol resin) was diluted with ethanol to a solids content of 40% foruse in the supply bath of FIG. 1 operated at 80 volts. The sameconcentrate without strontium chromate resin was diluted with water to asolids content of 10% for the electrocoating bath operated at 150 volts.The excess coating material in the rinse water could be removed usingthe process exemplified by FIGS. 3 and 4 and the solids content in therinse water bath should be about 0.2 to 5.0%.

Various modifications of the process and apparatus of the invention maybe made without departing from the spirit or scope thereof.

I claim:

1. A process for transferring non-conductive coating including anon-ionizable, electrophoretic, polymeric material into anelectrocoating bath comprising substantially the same polymeric materialwhich comprises immersing a transfer electrode coated with said coatinginto an electrocoating bath and removing said coating from the transferelectrode and applying it to a counter-electrode.

2. The process of claim 1 wherein the transfer electrode is coated in asupply bath.

3. The process of claim 2 wherein the transfer electrode acts as anodein one of the baths and as a cathode in the other bath.

4. The process of claim 3 wherein the deposit onto and removal of thecoating material from the transfer electrode is eifected at a voltage of0.1 to 100,000 volts.

5. The process of claim 3 wherein the coating material is deposited on acontinuous electrode as it passes through the supply bath and is removedfrom the continuous electrode as it passes through the electrocoatingbath.

6. The process of claim 3 wherein there is at least one transferelectrode which is conveyed via a suspension trolley from the supplybath into the electrocoating bath and back again.

7. The process of claim 3 wherein the articles to be coated in theelectrocoating bath act as counter-electrodes to the transfer electrode.

8. The process of claim 3 wherein stationary electrodes in theelectrocoating bath act as counter-electrodes to the transfer electrode.

1 2,453,757 11/1948 Renzoni 2o4-49 9. The process of claim 3 wherein thesolids content of the coating composition in the electrocoating bath isbetween 01-45% by Weight.

10. The process of claim 3 wherein the solids content of the coatingcomposition in 'the supply bath is between 0.170% by Weight.

References Cited UNITED STATES PATENTS 8/1965 Burnside et al 204-181 US.Cl. X.R.

